Modem indoor lighting systems serve a number of purposes, such as providing a comfortable lighting environment for the occupants of a room, and doing so efficiently. The typical indoor lighting environment may include one or more windows that contribute a varying amount of natural light to the environment of the room over time, and a number of light fixtures that provide sources of artificial light. Thus, a person at a workspace may experience periods of above average lighting in the environment and periods of below average lighting in the environment. In addition, different light fixtures placed across the room may provide different contributions to the lighting at the person's workspace. For example, light fixtures near the workspace may provide a larger contribution of lighting at the workspace than light fixtures farther away. Thus, it can be problematic to determine how different light sources (both artificial and natural) contribute to the lighting in the environment.